The present invention relates to a magnetic recording medium which comprises a biaxially oriented polyester film having an extremely low surface roughness and a magnetic layer formed on one side thereof, and which exhibits a high quality, a high density and an excellent travelling property even when it is not provided with a back coat layer.
More particularly, the present invention relates to a magnetic recording medium comprising a biaxially oriented polyester film which contains very fine particles and specific higher aliphatic carboxylic acids and/or derivatives thereof, and which exhibits specific average surface roughness, coefficient of friction and coefficient of friction during repeated travellings, and a magnetic layer formed on one side of the polyester film. The magnetic recording medium according to the present invention is excellent in electromagnetic characteristics, travelling property, wear resistance and scuff resistance even if it is not provided with a back coat layer, and can be produced at a low cost.
High-quality and high-density magnetic recording media, above all, video tapes have recently been increasingly developed. Specifically, as 1/2-inch video tapes for home use, tapes having a high S/N ratio which are called a super high grade or extra high grade type tapes have been chiefly used. In this type of video tapes, a film having an extremely small surface roughness is used as the base film in order to enhance the S/N ratio, and a back coat layer is generally provided on the opposite side of the magnetic layer, because stable travelling cannot be maintained by merely providing a magnetic layer on the base film.
However, formation of both of a magnetic layer and a back coat layer on the sides of a base film in the process of producing a magnetic tape requires an extra equipment and complicated steps which may lower the yield, resulting in a rise in the cost. Therefore, development of a magnetic recording medium has been strongly demanded, which has a base film having an extremely low surface roughness and is provided with fundamental properties of a magnetic tape such as stable travelling property, scuff resistance, prevention of producing white powder, etc. during the travel without a back coat layer.
As a result of researches to provide a magnetic recording medium which exhibits the above-described excellent properties without a back coat layer, the present inventors have found that a biaxially oriented polyester film which contains very fine particles and specific higher aliphatic carboxylic acids and/or derivatives thereof, and is obtained by an appropriate method, if necessary, can improve the slipping property in spite of an extremely low surface roughness thereof, and that a magnetic recording medium obtained by using this film as the base material exhibits a good electromagnetic converting property and stable travelling property, wear resistance and scuff resistance without a back coat layer. The present invention has been achieved on the basis of these findings.